Digital imaging • filmless imaging system • method of capturing a radiographic image with a sensor, breaking the image into electronic pieces and presenting & storing the image using a computer
Direct digital image production requires • x-ray source • digital intraoral sensor • computer • high-resolution monitor • software & printer
Digital intraoral sensor • small intraoral detector used to capture a radiographic image • when x-rays strike the sensor, an electronic charge is produced on the surface of the sensor, this electronic charge is digitized or converted to digital form • may be wired or wireless • sensor transmits information to computer
Pixel or picture element • discrete unit of information • consists of a small electron well where the x-ray or light energy is deposited upon exposure
(/digital image is composed ofpixejsh
• CCD (charge-coupled device)
(CCDTjHiarge-coupled device) • most common digital image receptor • in the intraoral sensor, a solid-state detector that contains a silicon chip with an embedded electronic circuit • sensitive to light or x-rays • 640 x 480 pixels in size
CMOS/APS (complementary metal oxide semiconductor/active pixel sensor)
•Jatest development in direct digital sensor tecnnSlogy • externally identical to CCD
i • differs in the way pixels are read • • advantages include lower production cost of
* the chip, lower power requirements & greater '. durability
• • smaUef.acjtive a r e a f ° r image acquisition
VCIDjJfcharge injection device) • another sensor technology • silicon based solid-state imaging receptor similar to CCD • no computer is required to process the images • system features CID x-ray sensor, cord and plug that are inserted into a light source on a camera platform
Advantages of digital imaging • superior gray scale resolution 256 shades of gray used instead of the 16-25 shades used with film • reduced exposure to radiation radiation exposure is 50% to 90% less than what is used to expose E-speed film • increased speed of image viewing images can be viewed instantly which allows for immediate intetpretation • lower equipment and film cost no need for purchase of film and related processing supplies and equipment • increased efficiency allows dental professionals to be more productive; image storage and communication are easier with digital networking • enhancement of diagnostic image features such as colorization and zooming allow for highlighting of conditions; the gray scale may be re-YSBjed. (digital subtraction) • effective patient education tool the size of images displayed monitor are easier for the patient to see; allows for chairside education and interaction
8
' superior gray-scale resolution ' reduced patient exposure to x-radiation > increased speed of image viewing > lower equipment and film costs ' increased efficiency ' effective patient education tool ' enhancement of diagnostic image
Disadvantages of digital imaging • sensor size some sensors are thicker and less flexible than film and may stimulate the gag reflex • initial set up costs significant initial cost for purchase of digital equipment as well as maintenance and repairs • resolution / image quality conventional x-ray film has a resolution of 12
•n - 20 lp/mm (linepairs per millimeter); digital Mmaging using a CCD has a resolution of 10
lp/mm; because human eye can only perceive 8 N>- 10 lp/mm — digital imaging performs at
least as well as traditional radiography • infection control some sensors cannot withstand heat steriliza-tion; barrier protection is required • wear & tear sensors are subject to damage, wear & tear and have a limited lifespan • legal issues because digital images can be enhanced, there may be legal implications
digital rad A method of obtaining a digital image where the sensor captures the image and immediately transfers it to a computer is termed:
indirect digital imaging
• direct digital imaging
• storage phosphor imaging
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digital rad A patient is extremely concerned about radiation exposure. Which of the fol-lowing is best for limiting the amount of exposure he will receive during a full mouth series?
• use of digital imaging
• use of E-speed films
• use of F-speed films
• substitute a panoramic image for the full mouth series
Digital imaging • filmless imaging system • methods of obtaining a digital image: direct and indirect
Direct digital imaging • required components - x-ray machine - intraoral sensor - computer & monitor • utilizes a sensor with a fiberoptic cable that is linked to a computer • sensor is placed intraorally and exposed to x-radiation • images are captured via a sensor (CCD, CMOS/APS or CID) • the sensor transmits the image to a computer monitor • images appear on monitor within seconds of exposure • software is used to enhance & store the image
Indirect digital imaging • scanning of traditional films • storage phosphor imaging
Scanning of traditional films • required components - CCD camera - computer & monitor • existing films are scanned and digitized using a CCD camera • CCD camera scans radiograph, converts the image and displays it on monitor • is inferior to direct digital imaging • image is a "copy" not an "original"
^Steage, phosphor imaging ss P£{> • required components
.-phosphor- coated plate - electronic processor/scanner - computer & monitor • a "wireless" digital imaging system • a reusable imaging plate coated with phosphors is used instead of a sensor with a fiberoptic cable • plates are similar to intraoral film in size, shape & thickness • image recorded on plate • after exposure, plate is placed in electronic processor where a laser scans the plate; image is transferred to the monitor within time frame nf'jQ.s.gcciridr1 to 5 minutes • also referred to as photo-stimulable phosphor imaging or PSP imaging
• use of digital imaging
Digital imaging • requires LESS radiation than conventional films because the sensor is more sensitive to x-rays than dental film • exposure time for digital imaging is approximately 5-0% less than what is required for F-speed film • intraoral, panoramic and other extraoral films may all be obtained digitally
Intraoral film speed • E-speed film is no longer available • Only D-speed film and F-speed film are available for use with intraoral radiography • F-speed film is recommended by the ADA
Q*^£^£Sdj!£2uj r e s 6p%_qf the exposure time of D-speed
Other ways to limit exposure to x-radiation • proper prescribing of dental radiographs based on individual needs of patient • use of lead apron & thyroid collar • use of proper dental x-ray equipment • use of rectangular position-indicating device (PID) • use of beam alignment devices • use of proper technique • proper sensor handing • proper image retrieval
image char A radiograph that exhibits areas of black and white is termed high contrast and is said to have a short contrast scale; a radiograph the exhibits many shades of gray is termed low contrast and is said to have a long contrast scale.
To limit image magnification, the longest target-receptor distance and short-est object-receptor distance are used. ^He
• both statements are true
• both statements are false
• the first statement is true, the second is false
• the first statement is false, the second is true
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image char Rank the following from LEAST radiopaque to MOST radiopaque.
contrast the difference in degrees of blackness (densi-tjg£) between adjacent areas on a dental radi-ograph.
• high contrast describes an image that ap-pears mostly black & white; shades of gray are absent
• low contrast describes an image with many shades of gray; few areas of black and white
scales of contrast the range of useful densities seen on a dental radiograph.
short-scale contrast describes a high contrast image with densities of black & white that results from using a .low kilovoltage. ^Mi l ium V ,
long-scale contrast describes a low contrast image with many shades of gray that results from using a highkilo-voltaee.
magnification a radiographic image that appears larger than the actual size of the object it represents; mag-nification is influenced by the target-receptor distance and the object-receptor distance.
target-receptor distance -• distance between the source of x-rays and the image receptor*film / W . * ^
• a longer PID results in a longer target-recep-tor distance and helps to limit magnification
object-receptor distance 's^*f- Q^* • distance between the tooth and the image
receptor • the closer the receptor is to the tooth, the less
magnification is seen on the image
to limit magnification • use a long target-receptor distance/I target-
receptor distance • use a short object-receptor distance/J, object
-receptor distance
bus cm i LOW CONTRAST •• LONG-SCALE CONTRAST
HV**t kvp 'image receptor=digital sensor or x-ray film
• sinus— bone— dent in— enamel fit
radiolucent structures • lack density • permit the passage of x-radiation • absorb very little x-radiation '.a.fj.o.w more x-rays to reach the receptor* • appear dark or black on an image
amalgam
radiopaque structures • are dense • resist the passage of x-radiation • absorb the x-radiation • allow few_xjay.s to reach the receptor • appear light or white on an image
Examples of radiolucent structures/mate-rials — BLACK or DARK
• air space images • soft tissue images • canals • foramens • fossas • sinuses • sutures • caries • pulp cavities • periodontal ligament space • denture acrylic • some composite restorations
Examples of radiopaque structures/mate-rials _ WHITE or LIGHT
LUCENT means TRANSPARENT and suggests something that lacks density — something that lacks density permits the pas-sage of x-rays & appears RADIOLUCENT
% S
OPAQUE means NOT TRANSPARENT and suggests something that is more dense — something that is more dense resists the passage of the x-rays & appears RA-DIOPAQUE
*receptot=digital sensor or x-ray film
misc. Dental radiographs are the legal property of the:
misc. A dental hygienist in your practice has an adult recall patient without evi-dence of caries who states she needs bite-wing x-rays because it has been 6 months since her last dental images. The hygienist should tell the patient that:
• yes, she is correct, it is time for new x-ray images
• bite-wings should be taken only once per year, not twice
• images should be taken based on patient need instead of a set time frame
Dental radiographs • original radiographs are legally the property of the dentist even though the patient or an insurance company may have paid for them • the radiographs are the property of the dentist because they are indispensable to the dentist as part of the patient record • radiographs should be kept indefinitely
Patient access to radiographs • patients have a right to reasonable access of their dental radiographs • access includes copies of original radi-ographs (not originals) forwarded to the dentist who will be responsible for the pa-tient's dental care
• dentist
Patients who refuse dental radiographs • when a patient refuses to have dental ra-diographs, the dentist must decide whether diagnosis and treatment can take place without the recommended radiographs • no document can be signed by the patient that releases the dentist from liability
Very important: the patient record, includ-ing radiographs, is legal documentation of a patient's condition.
Patient record must contain documentation of • informed consent • number & type of radiographs exposed • rationale for taking radiographs • diagnostic information obtained from in-terpretation
• images should be taken based on patient need instead of a set time
Prescribing dental radiographs • the dentist is responsible for prescribing the number, type and frequency of dental ra-diographs • each patient's condition is different and therefore each patient must be evaluated for radiographs on an individual basis • a radiographic examination should never include a set number and type of images at a set interval • guidelines for prescribing dental radiographs are published by the American Dental Association (ADA) in conjunction with the Food & Drug Administrations (FDA) • visit www.ADA.org for current guidelines • patients with caries, periodontal disease, tooth mobility, pain and impacted teeth need more frequent radiographic examinations
Guidelines for radiographs in the recall patient with clinical caries or risk of caries
• bite-wings at 6 - 12 month intervals with no clinical caries or risk of caries
• bite wings at 24 - 36 month intervals with periodontal disease
• clinical judgement for radiographs needed to evaluate periodontal disease; selected bite-wings & periapicals
normal anat The coronoid process often appears on what periapical image?
•maxillary incisor
• maxillary molar
• mandibular incisor
• mandibular molar
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Res Image 1- hamulus v
• a.k.a. hamular process • small, hook-like projection of bone • extends ..fmm the medial Pterygoid
jg|atejof^emsjp;hjenoidjbone • located posterior to the maxillary tuberosity • appears radiopaque • on a maxillary molar periapical image, appears as a hook-like radiopaque struc-ture • varies in length, shape & density • not always visible, depends on receptor placement
hamulus ' maxillary tuberosity
*b Image 2- maxillary tuberosity
• rounded prominence of bone that ex-tends distal to the third molar region • appears radiopaque • on a maxillary molar periapical image, appears as a rounded ra-diopaque bulge distal to the third molar region • varies in size, shape and density • not always visible, depends on re-ceptor placement
maxillary molar
Coronoid process • coronoid means "resembling the beak of a crow" • large prominence of bone on anterior ramus of mandible • is thin and triangular in shape • serves as an attachment site for one of the muscles of mastication • appears radiopaque • on a maxillary molar periapical image, appears as a beak-shaped radiopacity located inferior to, or superimposed over, the maxillary tuberosity • varies in shape and density • not always visible, depends on receptor placement
both statements are true Film processing converts the latent image to a visible image and preserves the image on film
Latent image • the film emulsion absorbs x:rays during ex-
jffgnni «r^ W e s the energy,within the silver halide crystals • the stored energy forms a pattern and creates an invisible image • the pattern of stored energy cannot be seen and is referred to as the latent image; it re-mains invisible until chemical processing
Black areas of the visible image • appear radiolucent f-;y • created by deposits of black metallic silver • structures that permit the passage of the x-ray beam allow more x-rays to reach the film & energize more silver halide crystals • more energized silver halide crystals result in more deposits of black metallic silver
White areas of the visible image • appear radiopaque ^?Ci • results from .unexposed silver halide crystals • structures that resist the passage of the x-ray beam restrict or limit amount of x-rays that reach the film resulting in no energized silver halide crystals and no deposits of black metal-lic silver
Film processing steps 1. development - developer solution removes halide portion of exposed silver halide crystals; this reduction of exposed crystals results in pre-cipitated.Wackjnel^icjy]yer (6^FJsJheopti-mal temperature for developer) 2. rinsing - water removes developer & stops development process 3. fixing - fixer solution removes unexposed sil-ver halide crystals & hardens the film 4. washing - water removesaTTexcess chemi-cals from the emulsion 5. drying
Cdroquinone & cloijj hydroquinone slpjvly con-verts silver halide crystals & generates black tones ;elon-quickly converts silver halide crys-tals & generates gray tones • preservative is Sodium sulfite; prevents oxi-dation of developer agents • accelerator is sodium carbonate; activates the developer & softens emulsion
^ ^t^*-*******««..«——"""-'^
• restrainer ts;potassium bromide; prevents developer from deveToping unexposed crystals
Fixer composition • fixing agent (a.k.a. clearing agent or hypo) is^xliu^Jhiojul&teorammonium thiosulfate; removes or clears" all un-exposed & underdeveloped silver halide crystals from emulsion; clears the film so that black image produced by the devel-oper can be seen • preservative is,si»{Uumjmlfite (same as in developer); prevents the deterioration of the fixing agent • hardening agent is potassium alum; shrinks and hardens the gelatin in the emulsion • acidifier is a c j ^ j i c id j ) r sulfuric acid; neutralizes the alkaline developer and stops development process & provides necessary acidic environment for fixer
Safelighting • lighting that is required in darkroom for safe illumination while processing x-ray film
QJ^JJQdak^BXdt£S^hMM?r with a 15-watt bulb at least 4 feet away from working surface
• fixing agent
Film processing steps 1. development 2. rinsing 3. fixing 4. washing 5. drying
Manual film processing • a.k.a. hand processing or tank processing • method used to process films where all steps are performed manually • equipment needed includes processing tanks with covers, thermometer, timer, film hangers and stirring rod • typical processing times include: 5 minutes in developer —> 30 second rinse —> 10 minutes in fixer —• at leastdQanm-utgsjriwash • as a rule, fixing time is twice as long as developing time
Automatic film processing • method used to process films using where all steps of film processing are au-tomated • automatic processor is required • total processing time is 4-6 minutes
processing Your assistant has processed three panoramic films today. She noticed the films are progressively getting lighter and lighter. What should be done to correct the problem?
• decrease the temperature of the developer
• increase the temperature of the fixer
• replenish the developer
• process the films a second time
• decrease the time in the developer
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processing Your assistant has just processed a film that appears too dark. Identify each of the potential causes of this problem.
• inadequate time in developer
• excessive time in developer
• developer solution too cool
• developer solution too hot
• depleted developer
• concentrated developer
RADIOLOGY 32
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' replenish the developer
Replenisher solutions • a replenisher is a superconcentrated solu-tion that is added to the existing processing solutions to compensate for the loss of vol-ume and strength that occurs due to oxida-tion
• ' :-r' • both the developer and fixer must be re-plenished daily to maintain adequate fresh-ness • replenishment maintains adequate con-centrations of chemicals which ensures uni-form processing • failure to use replenishing solutions results in non-diagnostic radiographs
Processing solutions • include developer, fixer & replenisher • must follow manufacturer directions for storage, mixing & replenishing • the developer and fixer must be changed at the same time every 3-4 weeks or more often with high volume of processing • tanks must be scrubbed and cleaned when changing solutions
Developer solution life is affected by • cleanliness of tank • size of films processed • number of films processed • temperature • evaporation
Depleted developer • is weakened, lacks concentration • does not fully develop the latent image • produces a non-diagnostic image with red-uced density and contrast • results in underdeveloped films • underdeveloped films appear light
Underdeveloped film • appears light • causes
- time/inadequate time in developer - temperature/developer too cool - concentration/depleted developer
• solutions - time/! time in developer - temperature/t temperature - concentration/replenish developer
• excessive time in developer • developer solution too hot • concentrated developer
Time and Temperature: Problems and Solutions
Example
Underdeveloped film
Overdeveloped film
Reticulation of emulsion
Appearance
Light
Dark
Cracked
Problems
- Inadequate development time - Developer solution too cool - Inaccurate timer or thermometer - Depicted or contaminated developer solution
- Excessive developing time - Developer solution too hot - Inaccurate timer or thermometer - Concentrated developer solution
Sudden temperature change between developer and water bath
Solutions
- Check development time - Check developer temperature - Replace faulty timer or thermometer - Replenish developer with fresh
solutions as needed
- Check development time - Check developer temperature - Replace faulty timer or thermometer - Replenish developer with fresh
solutions as needed
Check temperature of processing solutions and water bath; avoid drastic temperature differences
Reprinted from Iannucci, Joen M. and Laura Jansen: Dental Radiography Principles and Techniques. Fourth Edition, d from Elsevier Saunders
2012, with permission
processing Black branching lines appear on a processed him. Which of the following is the most likely cause?
Exposure measurement • exposure refers to the measurement of ion-ization in air produced by x-rays • roentgen (R) is a way of measuring radia-tion exposure by determining the amount of ionization that occurs in air • R is limited to measurement in air • there is no SI unit for exposure that is equiv-alent to the R • exposure expressed in Coulombs per kilo-gram (C/kg)
Dose measurement • dose refers to amount of energy absorbed by a tissue • rad is a unit of absorbed dose that is equal to the deposition of 100 ergs/g of tissue • the SI unit for rad is gray (Gy)
Dose equivalent • rem is traditional unit of dose equivalent used to compare the biologi&.£ffects_of dif-ferent Jypes of radiation on a tissue or organ • is the product of Gy x QF (quality factor) specific for the radiation type • for x-rays, QF=1
5Tumt for rem is sievert (Sv)
Uni t Definition Convers ion
Traditional System (older system) roentgen (R)
radiation absorbed close (rad)
1 rem = rads X QF roentgen equivalent (in) man (rem)
SI system (newer system)
lR = 87erg/g
1 rad = 100 erg
1R = 2.58X10 "'C/kg
1 rad = 0.01 Gy
Coulombs per kilogram (C/kg)
gray (Gy)
sievert (Sv)
1 Gy = 0.01 J/kg
l S v = G y X Q F | 1
1 rem = 0.01 Sv
1 C/kg = 3880 R
is*si« 10 rads
: Sv = 100 rerh>
rad biology List the following cells from most RADIORESISTANT to most RADIOSENSITIVE.
rad biology After the bombings of Hiroshima, there were many persons exposed to radi-ation. Symptoms such as hair loss did not occur until days following the ex-posure. The time between exposure and onset of symptoms is termed:
• all ionizing radiations are harmful to living tissues • radiation produces chemical changes that results in biologic damage in living tissues • not all cells respond to radiation in the same manner • cells respond to radiation based on mi-totic activity, differentiation and cell metabolism • cells that are dividing and immature are most susceptible to radiation
• radiosensitive cells are susceptible to ra-diation exposure • the most radiosensitive cell is the small lymphjaq&e • radioresistant cells are resistant to radi-ation exposure • the most radioresistant cells are muscle anrlnjejye • radiation effects are classified as somatic (occur in person irradiated) or genetic (passed on to future generation)
Sensitivity Radiosensitive Radioresistant Cells Sensitivity high
high
high
high
fairly high
fairly high
fairly high
small lymphocyte
bone marrow
reproductive cells
intestinal mucosa
skin
lens of eye
oral mucosa
muscle tissue
nerve tissue
mature bone/cartilage
salivary gland
thyroid gland
kidney
liver
low
low
fairly low
fairly low
fairly low
fairly low
fairly low
latent period
Mechanisms of radiation injury • ionization & free radical formation are re-sponsible for cell injury • free radical formation is the primary mecha-nism responsible for damage
Theories of radiation injury • direct theory - cell damage results when ra-diation directly hits critical areas within the cell & direct alteration of the cell occurs • indirect theory - suggests that x-ray photons are absorbed within the cell and cause the for-mation free radicals & toxins which result in cell damage K- f*W+$wa - ^W, W * eeAi,
Dose-response curve • a dose-response curve is used to demonstrate the response of tissues to the dose of radiation received • a threshold dose does not exist & response of tissues is directly proportional to the dose • injury from radiation depends on total dose,
.„dose ratej^anjount of tissue affected, cgjl sen-sitivity and age
Stochastic & nonstochastic effects • stochastic effects occur as a direct function of dose (cancer, genetic mutations) • nonstochastic effects have a threshold and in-crease in severity with increased dose (hair loss, decreased fertility)
Radiation injury sequence • latent period - period of time between exposure and onset of symptoms • period of injury - follows latent period and may result in cell death, change in cell function or ab-normal mitosis • period of recovery - follows injury; depending on a number of factors, cells can repair the damage caused by radiation
Radiation effects • short term effects occur when large amounts are absorbed in a short period of time (not applicable to dentistry) • long term effects occur when small amounts are absorbed over a long period of time; linked to in-duction of cancer, birth & genetic effects • cumulative effects occur; radiation damage is ad-ditive and unrepaired damage accumulates in the tis-sues and leads to health problems (cancer, cataract formation, birth defects)
Radiation effects on cells • the cell nucleus is more sensitive to radiation than cytoplasm; DNA is affected • cell division is disrupted which may lead to dis-rupted cell function or cell death • radiation causes cell death by damaging chromo-somes
rad biology A patient with a large squamous cell carcinoma of the lateral border of the tongue is scheduled for a radical neck dissection. Prophylactic extractions of hopeless teeth must be done to prevent which of the following?
Definition • most serious possible complication facing the oral cancer patient • condition of non-vital bone in a site of radio-therapy; bone dies as a complication of radio-therapy • is not an infection
Cause • radiation therapy destroys cancerous cells but also destroys normal cells, damaging small ar-teries and reducing circulation • insufficient blood supply to the irradiated area decreases the ability to heal, and any subse-quent infections to the jaw can pose a huge risk to the patient • patients receiving high dQjt££_Qf,xadiation £>40 Gv) to the jaw area are at risk
Histologic features- 3 H's v* hypocellular bone v^hypovascular tissue
v""hypoxic tissue & bone
Prevention • extract all hopeless teeth 3 weeks prior to ra-diotherapy • if extracting after radiotherapy, use of systemic antibiotics is warranted • hyperbaric oxygen treatments before and after radiotherapy may be helpful
• osteoradionecrosis
Clinical features • may involve the maxilla or mandible • more common in the mandible • most frequently occurs when an insult to the bone is sustained in the irradiated area, such as related subsequent surgery, biopsy, tooth extractions or denture irritations • may also be precipitated by periodontal disease or occur spontaneously • symptoms may include pain, swelling, reduced mobility, drainage, exposed bone in the involved area and destruction of bone • symptoms may occur months or years after the radiotherapy
Management • difficult to manage • prevention is key • debridement of infected bone may be required • advanced cases may require radical surgery • patients must be followed closely by physicians and dentist regularly
• both statements are true
Radiation therapy of oral cavity • used to treat radiosensitive oral malignant tu-mors, usually squamous cell carcinoma • indicated when the tumor is radiosensitive, advanced, or, cannot be treated surgically be-cause it is deeply invasive • fractionation
- total radiation dose is delivered in smaller multiple doses
- provides greater tumor destruction than a sin-gle large dose
- allows for increased cellular repair of nor-mal tissues
- increases mean oxygen tension resulting in tumor cells that arc more radiosensitive
W M M I M M n
Radiation effects on the teeth • irradiation of developing teeth severely retards growth • adult teeth are radioresistant\3^<'
Radiation effects on bone • irradiation of bone results in damage to the fine vasculature • normal marrow may be replaced with fatty maiTOW or fibrous connective tissue • necrosis may occur and exhibits loss of os-teoblastic and osteoclastic activity
Radiation effects on oral tissues Ks • occurs by end of 2nd weekpf therapy *5»jf • mucositis results; appears as areas of redness and inflammation • as therapy continues, the oral tissues break down resulting in formation of white pseudomembranes • oral condition worsens with continued therapy and candidiasis often occurs • following therapy, oral tissues heal within ap-proximately 2 months ifogut 8
Radiation effects on taste buds /-' • taste buds are radiosensitive • radiation therapy damages taste buds • a loss of taste may first occur during the 2nd or 3rd week of radiation therapy
Radiation effects on salivary glands • radiation therapy damages salivary gland tissues • there is a marked & progressive loss of salivary secretion; extent of reduced flow is dependent on dose • causes decreases in saliva, pH & buffering ca-pacity • causes increased viscosity • dry moutn (xerostomia) results & makes the pa-tient susceptible to radiation caries - a rampant form of caries • xerostomia causes tenderness of oral tissues and difficulty in swallowing
rad char In the dental x-ray tube, the number of electrons flowing per second is meas-ured by:
rad char When the PID length is changed from 8" to 16", the target-receptor distance is doubled. According to the Inverse Square Law, the resultant x-ray beam is:
• 1/4 as intense
• 1/8 as intense
• four times more intense
• eight times more intense
• none of the above
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RADIOLOGY
W ~ TJu^-^ milliamperage (mA) ^rrv*4
^ V t i x_ray beam intensity
time and distance
x-ray beam quality & kVp • quality refers to the average energyor 7 ^ intensity is the total energy contained in penetrating power of the x-ray beam and the x-ray beam at a specific area at a given is controlled by the kilovoltage peak (kVp) time • kVp controls the speed & energy of the ~ Qrfntensity is affected by kVp, mA, exposure electrons and determines the penetrating power of the beam £> • kVp range for dental radiography is A s^^k ^
c^iookv^i Tt<y x-ray beam quantity & mA ™ « - * .
• quantity refers to the number of x-rays J ^ ^ H , a*1
produced and is controlled by the mil-' e\^l% liamperage (mA) • mA controls the amperage of the fila-ment current and the amount of electrons that pass through the filament • mA controls the temperature of the fil-ament • as the mA increases, more electrons pass through the filament and more x-rays are produced •JTIA range for dental radiography is
j ^ l 5 m A P ^"T iHmmi in i iM urn-
to remember, think alphabetical order ... kVp= quality ( k & 1) mA = quantity ( m & n )
Adjustment T 1 r i T i
kVp
kVp
mA
mA
time
time
Film appears
darker
lighter
darker
lighter
darker
lighter
to INCREASE film density & make it darker, INCREASE:
• mA •kVp • time
to DECREASE film density & make it lighter, DECREASE:
• mA •kVp • time
Inverse Square Law • defined as: the intensity of the radiation is inversely proportional to the square of the distance from the source of radiation • inversely proportional means that as one variable increases, the other decreases • when the target-receptor distance is in-creased, the intensity is decreased
original intensity . new intensity new distance2 original distance2
Example: If the PID length is changed from 8" to 16", how does this increase in target-receptor distance af-fect the intensity of the beam? plug numbers into the mathematical for-mula:
x / 8 2 4* /UK \IW solve for x
1 / x= 162 / 82
1 / x= 256 / 64 1 / x= 4 / 1
x= 1/4 answer • doubling the distance results in a beam that is % as intense • the x-ray beam that exits an 8" PID is more intense than one the exits a 16" PID (see dia-gram)
The distance traveled by the x-ray beam affects the intensity; distances to be considered include the following:
• target-surface distance is the distance from the source of radiation to the surface of the pa-tient's skin • target-object distance is the distance from the source of radiation to the tooth • target-receptor distance is the distance from the source of radiation to the receptor ffilm or sensor)
rad char A 6'5" muscular male with a large mandible requires a complete series of den-tal images. You plan to increase the kVp because of his size. Identify each of the following that results with the increased kVp:
Increased kVp • produces x-rays with increased energy (speed) and shorter wavelength • increases the penetrating power of the x-ray beam • is needed for larger patients with large bones and significant amounts of soft tissue • results in increased density (makes image darker) • results in reduced or low contrast which is long-scale contrast
Contrast • refers to how sharply dark and light areas are separated or differentiated on an image • the difference in degrees of blackness be-tween adjacent areas on a dental radiograph
• a more penetrating beam • a reduced subject contrast • long scale contrast
Long-scale contrast • LONG scale = JLOW contrast = LOTS of gray
• a low contrast image exhibits many shades of gray • a low contrast image does not exhibit black & white
Adjustment
T (High)
4 (Low)
kVp
kVp
Contrast scale
LONG lots of gray
SHORT black & white
Contrast
LOW
HIGH
Contrast & kVp • adjustment of kVp affects contrast • with low kVp (65-70), a high contrast image results • with high kVp (90), a low contrast image results
Patient size & kVp • large patients need increased kVp; if not increased — image appears LIGHT • small patients need decreased kVp; if not decreased — image appears DARK
Density description • a visual characteristic of a radiographic image • overall blackness or darkness of an image • when a dental image viewed, the relative transparency of areas depends on the distri-bution of black silver particles • density is the degree of.silver blackening • an image of correct density allows one to view the black areas (air space images), white areas (enamel, dentin, bone) and gray areas (soft tissue)
Factors that influence density • exposure factors
-kVp - mA - exposure time
• thickness of subject adjustments in kVp, mA and exposure time can be made to compensate for size variations • an increase in any exposure factor , sepa-rately or combined, increases the density of an image
\9
Adjustment
T 4 r 4. T 4 t
x4
kVp
kVp
mA
mA
time
time
thickness
thickness
• • .
kVp mA exposure time
Densitv Film
t 4 t 4 T 4 4 T
appears darker
lighter
darker
lighter
darker
lighter
lighter
darker
Size of patient • thickness of subject also affects density; with a large patient (thick bones, excess soft tissue), fewer x-rays reach the receptor and as a result, the image appears lighter • with increased thickness, a decreased den-sity results • with decreased thickness, an increased density results
Note: the use of a 2-film packet does not affect the density of the image
rad physics Which of the following converts electrons into x-rays?
rad physics Which of the following focuses the electrons into a narrow beam and directs the beam across the tube toward the tungsten target of the anode?
X-ray tube • heart of the x-ray generating system • critical to the production of x-rays • glass vacuum tube from which all the air has been removed • component parts include leaded glass hous-_ing, negative cathode & positive anode
Leaded-glass housing • leaded-glass vacuum tube that prevents x-rays from escaping in all directions • a "window" permits the x-ray beam to exit the tube
| Cathode/negative electrode! • supplies electrons necessary to generate x-rays • consists of a tungsten wire filament in a molybdenum cup-shaped holder • tungsten filament (coiled tungsten wire) produces electrons when heated • molybdenum cup focuses the electrons into a narrow beam and directs the beam across the tube toward the tungsten target of the anode
A n o node/positive electrode •ode isTnto x-• converts electronslivto x-ray photons
• consists of a wafer-thin tungsten plate em-bedded in a solid copper rod • tungsten target serves as a focal spot and converts bombarding electrons into x-ray photons • copper stem functions to dissipate the heat away from the tungsten target
molybdenum cup
Production of x-rays • tungsten filament is heated and electrons are produced • molybdenum cup focuses the electrons into a narrow beam and directs the beam to-wards the tungsten target in the anode • x-rays are generated when the beam is sud-denly stopped by the tungsten target •4fafi.en£igy_of motion is converted to x-ray energy (1%) and heat (99%) • insulating oil that surrounds the x-ray tube absorbs the heat • x-rays that are produced are emitted in all directions; leaded-glass housing of tube pre-vents the x-rays from escaping • small number of x-rays exit the x-ray tube through the unleaded glass window area • x-rays travel through unleaded glass win-dow, through the tubehead seal and then the aluminium disks • the lead collimator restricts the size of the beam and the x-ray beam travels down the lead lined position -indicating device (PID) and exits at the opening
Component functions • tungsten filament of cathode produces electrons when heated • molybdenum cup of cathode focuses the electrons into a narrow beam and directs the beam towards the tungsten target in the anode • tungsten target in anode stops the elec-trons and converts the energy into x-rays & heat •(copper stenijjserves to dissipate the heat that is createdwith the production of x-rays
|i_Metal ji housing £ of x-ray 1 tube-1
J a-lnsulating : oil
K. . -Lead Unleaded glass collimator window of
x-ray tube 'osition
indicating device
rad physics Identify each of the following that are properties of x-rays:
• no weight
• travel at speed of sound
• have no charge
• cannot be deflected or scattered
• are invisible
• are absorbed by matter
• do not damage living cells
• do not cause fluorescence 45
copyright O 2013-2014- Dental Decks
RADIOLOGY
rad physics Rectification is the conversion of a direct current (DC) to an alternating cur-rent (AC).
The dental x-ray tube acts as self-rectifier in that in changes DC to AC while producing x-rays.
• both statements are true
• both statements are false
• the first statement is true, the second is false
• the first statement is false, the second is true
46 copyright ® 2013-2014- Dental Decks
RADIOLOGY
Properties of x-rays
• appearance invisible and cannot be detected by any of the senses • mass have no mass or weight • charge have no charge • speed travel at the speed of light • wavelength travel in waves and have short wave-lengths with a high frequency\V"" • path of travel travel in straight lines and can be de-flected, or scattered • focusing capability cannot be focused to a point and al-ways diverge from a point
• no weight • have no charge • are invisible • are absorbed by matter
• penetrating power can penetrate liquids, solids, and gases; the composition of the substance deter-mines whether x-rays penetrate or pass through, or are absorbed • absorption absorbed by matter; the absorption de-pends on the atomic structure of mat-ter and the wavelength of the x-ray • ionization capability can interact with materials they pene-trate and cause ionization • fluorescence capability can cause certain substances to fluo-resce or emit radiation in longer wave-lengths (e.g., visible light and ultraviolet light) • effect on film can produce an image on photographic film • effect on living tissues cause biologic changes in living cells
• electricity is the energy used to make x-rays; electrical energy consists of a flow of electrons through a conductor; this flow is known as the electrical current • electrical current is termed direct current (DC) when the electrons flow in one direc-tion through the conductor • alternating current (AC) describes an elec-trical current in which the electrons flow in two, opposite directions • rectification is the conversion of AC to DC • dental x-ray tube acts as a self-rectifier in that it changes AC into DC while producing x-rays; ensures that current is always flowing in the same direction from cathode to anode • amperage is the measurement of the num-ber of electrons moving through a conductor,^, c7irrentls~measured in amperes (A) or mil-liampcres (mA) • voltage is the, measurement of electrical force that causes electrons to move from a negative pole to a positive one; measured in volts (V) or kilovolts (kV) • circuit is a path of electrical current; two electrical circuits are used to produce x-rays: a low-voltage/filament circuit and a high-voltage circuit
* % .
• both statements are false
• low voltage/filament circuit uses 3 to 5 volts, regulates the flow of electrical current to the filament; controlled by mA settings • high-voltage circuit uses 65,000 to 100,000 volts, provides the high voltage required to accelerate; controlled by kVp settings • transformer is a device that is used to either increase or decrease the voltage in an electri-cal circuit; it alters the voltage of the incom-ing current and then routes the electrical energy to the x-ray tube; three types of trans-formers are used to adjust the electrical cir-cuits (see below) • step-down transformer is used to decrease the voltage from the incoming 110- or 220-line voltage to the 3 to 5 volts used by the fil-ament circuit • high-voltage circuit uses both a step-up transformer and autotransformer • step-up transformer is used to increase the voltage from the incoming 110- or 220-line voltage to the 65,000 to 100,000 volts used by the high-voltage circuit • autotransformer serves as a voltage com-pensator that corrects for minor fluctuations in the current
rad physics Which of the following occurs only at 70 kVp or higher and accounts for a very small part of the x-rays produced in the dental x-ray machine?
Types of x-rays • not all x-rays produced in the x-ray tube are the same; x-rays differ in energy and wave-length • energy and wavelength varies based on how the elections interact with the tungsten in the anode • kinetic energy_of electrons isconverted to x-ray photons via general (braking or Brem-sstrahlui'g) radiation or characteristic radiat-ion • general/braking radiation is produced when speeding electrons slow down due to in-teractions with the nuclei of the tungsten tar-get atoms
- braking refers to the sudden stopping or slowing of high-speed electrons when they hit or come close to the tungsten target - 70% of the x-ray energy produced is gen-eral radiation
• characteristic radiation is produced when a high-speed electron dislodges an inner-shell electron from the tungsten atom and causes ionization " I - the remaining electrons rearrange to fill the vacancy resulting in a loss of energy & pro-duction of x-ray photon
- only a small % of x-rays produced; occurs only at > 70 kVp
Definitions • primary radiation is the penetrating x-ray beam that is produced at the target of the anode and exits the tubehead; a.k.a. primary or useful beam • secondary radiation is x-radiation that is created when the primary beam interacts with matter; ig less penetrating thanprimaryradia-tion • scatter radiation, a form of secondary rad-iation, is the result of an x-ray deflected from its path by the interaction with matter; deflect-ed in all directions by the patient's tissues; detrimental to tissues • id Compton scatter] ionization takes place;
& \§ an x-ray photon collides with an n outer-shell C *> > electron and gives up part of its energy to
'£% eject the electron from its orbit; x-ray photon •*J*Hoses energy and continues in a different dir-
% ection (scatters) at a lower energy level; ac-counts forJ>2% of the scatter that occurs • coherent or unmodified scatter occurs when a low-energy x-ray photon interacts with an outer-shell electron; no change in the atom occurs; x-ray photon of scattered radiat-ion is produced; x-ray photon is scattered in a different direction from that of the incident photon; noJoss of energy and no ionization occur; accounts for 8% of the interactions
insulating oil < unleaded glass window ' tubehead seal
• inherent filtration takes place when the primary beam passes through the glass window of the x-ray tube, the insulating oil, and the tubehead seal • inherent filtration of the dental x-ray machine is approximately 0.5 to 1.0 milli-meter (mm) of aluminum • inherent filtration alone does not meet the standards regulated by state and federal laws; added filtration is required
• added filtration refers to the placement of aluminum discs in the path of the x-ray beam between the collimator and the tubehead seal • aluminum discs can be added to the tubehead in 0.5 mm increments • purpose of the aluminum discs is to fil-ter out the longer-wavelength, low-en-ergy x-rays from the x-ray beam • low-energy, longer wavelength x-rays are harmful to the patient and are not useful in diagnostic radiography • filtration of the x-ray beam results in a higher energy & more penetrating useful beam • state and federal laws regulate the re-quired thickness of total filtration = in-herent filtration + added filtration • dental x-ray machines operating at ,< 70 kVp require a minimum total of 1.5 mm aluminum filtration • dental x-ray machines operating at > 70 kVp require a minimum total of 2.5 mm aluminum filtration
rad protection Identify each of the following that is recommended for operator protection during exposure.
• stand 3 feet away from x-ray tubehead
• stand at a 45-75 degree angle to the beam
• wear a lead apron
• stand behind a barrier
• hold the PID
• hold the film if the patient cannot stabilize it
rad protection Prior to x-ray exposure, the proper prescribing of radiographs and the use of proper equipment can minimize the amount of radiation that a patient re-ceives.
Radiographs must be prescribed by the dentist based on the individual needs of the patient.
• both statements are true
• both statements are false
• the first statement is true, the second is false
• the first statement is false, the second is true
rad protection Prior to x-ray exposure, the proper prescribing of radiographs and the use of proper equipment can minimize the amount of radiation that a patient re-ceives.
Radiographs must be prescribed by the dentist based on the individual needs of the patient.
• both statements are true
• both statements are false
• the first statement is true, the second is false
• the first statement is false, the second is true
Operator protection guidelines • must use proper protection during exposure to avoid the primary beam, scatter radiation etc. • must avoid the primary beam • distance, position and shielding are all im-portant for protection
Distance recommendations • must stand at least 6' away from the tube-head • if distance is not possible, a protective bar-rier must be used
Primary beam
Y '
".••••.. ' -:.,.\:.-: ••:.::•.-::•• ' $ 'l W'
Radiographer
135"
Reprinted from Iannucci, Joen M. and Howerton, Laura Jansen: Dental Radiography Principles and Techniques. Fourth edition •D 2012 with permission from Elsevier-Saunders.
• stand behind a barrier Position recommendations
• must stand perpendicular to the primary beam, or, at a £0-135 degree angle to the beam " ' • • never hold a film in place for a patient dur-ing exposure • never hold the PID during exposure
Shielding recommendations • whenever possible, stand behind a protec-tive barrier, such as a wall
Maximum permissible dose (MPD) • MPD is the dose of radiation the body can endure with little or no injury • for non-occupationally exposed person limit is 0.001 Sv/year • for occupationally exposed person limit is 0.05 Sv/year • for occupationally exposed pregnant person — limit is 0.001 Sv/year
ALARA concept •As Low As Reasonably Achievable concept states that all exposure to radiation must be kept to a minimum • applies to patients & operators
Patient protection before exposure • proper prescribing of dental radi-ographs • use of proper equipment including filtration, collimation and PID • the rectangular PID (instead of round) is most effective in reducing pa-tient exposure • use of a long PID is more effective than use of a short PID
Patient protection during exposure • use of thyroid collar for intraoral films and lead apron for all films • use of digital imaging or use fastest film available (F-speed) • use of beam alignment devices • use of correct exposure factors (kVp, mA & exposure time) • use of proper technique
• both statements are true
Patient protection after exposure • proper sensor or film handling • proper image retrieval or film pro-cessing
Guidelines for prescribing of dental radiographs
• dentist is responsible for ordering im-ages & uses professional judgment to make decisions concerning the num-ber, type and frequency of dental radi-ographs • radiographic exam should never in-clude a predetermined number of films • radiographs should never be taken at predetermined time intervals • radiographs should be ordered based on the individual needs of the patient • guidelines for prescribing dental ra-diographs have been determined by the ADA and FDA
rad protection Which of the following is used to restrict the size and shape of the x-ray beam and to reduce patient exposure?
• aluminum discs
• collimation
• inherent filtration
• total filtration
51 copyright €> 2013-2014- Dental Decks
RADIOLOGY 51
tech If a processed film appears light with herringbone or tire track pattern on it, which of the following is the likely cause?
• the film was bent during placement
• the film was reversed (placed backwards) during exposure
Collimation • used to restrict the size and shape of the x-ray beam & to reduce patient exposure • a collimator is a lead plate with hole in the middle, is fitted over the open-ing of the machine housing where the beam exits • collimator may have a round or rec-tangular opening • rectangular collimator restricts the size of the beam to slightly larger than a size 2 film and significantly re-stricts patient exposure • circular collimator produces a cone shaped beam & restricts the size of the beam to 2.75" in diameter • when using a circular collimator, fed-eral regulations re quire that the beam be restricted to 2.75" as it exits the PID and reaches the skin of the pa-tient
Position indicating device (PID) • the PID or cone is an extension of the x-ray tubehead used to direct the beam • types of PID include conical, round and rectangular • a conical PID is a closed plastic cone that produces scatter radiation;no longer used in dentistry • a round PID is a tubular open ended lead- lined extension; no PID scatter is produced • a rectangular PID is a rectangular open ended lead-lined extension; is most effective in reducing patient ex-posure; no PID scatter is produced • both round and rectangular PIDs are available in two lengths: short (8") and long (16")
^"VtMJangPID is preferred because less V'uivergence of me*x-ray beam occurs
• the film was reversed (placed backwards) during exposure
A reversed film is light &
exhibits a herringbone
pattern.
A double exposure appears dark & exhibits a double image.
A bent film appears stretched & distorted. With movement of the patient or PID, a blurred image results.
Magnification • enlargement of an image that results from the divergent paths of x-ray beam • some degree of magnification is pres-ent in every image due to divergent paths • influenced by target-receptor distance and object-receptor distance • target-receptor distance (or source to receptor distance) is the distance be-tween the source of x-rays & image re-ceptor • PID determines target-receptor distance • shorter PID results in more magnifi-cation; longer PID results in lessjnagni-
JBcatjori • object-receptor distance is the dis-tance between the tooth & image recep-tor • if there is decreased distance between the tooth & receptor, less magnification occurs • if there is increased distance between the tooth & receptor, more magnification occurs
Focal spot size • tungsten target in anode is focal spot • size ranges from0.6 -1.0 minj^nd is de-termined by the manufacturer (cannot be controlled by operator) • the size of focal spot influences the image sharpness • the smaller the focal spot, the sharper the image
In dental radiography, the most accurate image:
• use the smallest focal spot size • use the LONGEST target-receptor dis-tance • use the SHORTEST object-receptor distance • direct the central ray of the x-ray beam perpendicular to the receptor and tooth • keep the receptor parallel to the tooth being imaged
• vertical angulation is insufficient/too flat
Vertical angulation • refers to the positioning of the PID in a vertical, or up-and-down plane • correct vertical angulation results in an image that is the same length as the tooth • incorrect vertical angulation results in ELONGATION or FORESHORTENING • an elongated image appears long & results from too flat vertical angulation • a foreshortened image appears short & re-sults from too steep vertical angulation • 0 degree vertical angulation = PID parallel with floor • positive vertical angulation = PID pointing DOWN to floor/PID above occlusal plane • negative vertical angulation = PID point-ing UP to ceiling/PID below occlusal plane H
Vortical angulation • refers to the positioning of the PID in a horizontal or side-to-side plane • when tire central ray is directed through the interproximal contacts of the teeth, correct horizontal angulation results and open con-tacts on seen the dental image • incorrect horizontal angulation results in overlapped contacts (contacts are superim-posed over each other)
ELONGATION results when the vertical angula-tion is TOO FLAT; teeth look long & stretched
FORESHORTENING results when the vertical angulation is TOO STEEP; teeth look short
chin tipped too far downward \ / (see image on reverse side)
• mandibular incisors appear blurred • loss of detail in anterior apical region • condyles may not be visible • results in severe interproximal over-lapping • occlusal plane has excessive upward curve • exaggerated smile line is seen
chin tipped too far forward A (see image below) ' ^
• hard palate & floor of nasal cavity ap-pear superimposed over maxillary teeth • maxillary incisors appear blurred • maxillary incisors appear magnified • occlusal plane downward curve • reverse smile line (frown) is seen
film bending Film bending
• images appear stretched & distorted • occurs due to curvature of hard palate
Film creasing • crease appears as a thin black line • represents where the emulsion of the film has cracked
Phalangioma • the bone of the patient's finger seen on the image • results when finger is in front of the receptor instead of behind it (seen with use of bisecting technique where patient holds the film— not recommended)
Light film • may result from underexposure— too short of exposure time, too low kVp or too low mA
Dark film • may result from overexposure - too long of exposure time, too high kVp or too high mA
Fogged film -s^-""" • appears gray & lacks contrast • occurs when film is exposed to radiation other than primary beam (e.g., scatter) • may result from improper safelighting or light leaks in dark room
tech Use the two images below to determine the spatial position of the round ob-ject. Following the exposure of image #1, the x-ray tubehead was moved and the beam was directed from a mesial angulation in image #2. Given this in-formation, where is the round object located?
• if the central ray is not directed through the interproximal contacts of the teeth, the horizontal angulation is incorrect • incorrect horizontal angulation results in overlapped contacts seen on the image
Cone-cut • if the beam is not centered over the recep-tor, a clear unexposed area or cone-cut is seen on the image • the PID or "cone" is said to "cut" the image • a cone-cut may occur with the use of a rect-angular or round PID • a conecut may occur with or without the use of a beam alignment device
poor receptor placement • a periapical image shows the entire tooth and root, including the apical area and must be placed to cover those areas • incorrect periapical receptor placement may result in absence of apical structures or a tipped or tilted occlusal plane • a bite-wing image shows the crowns of both the maxillary and mandibular teeth, the inter-proximal areas and crestal bone • incorrect bite-wing receptor placement may result in absence of teeth or teeth surf-faces on an image, tipped occlusal plane
Incorrect hori-zontal angulation results in over-lapped contacts.
If the beam is not cen-tered over the recep-tor, a cone-cut results & a clear unexposed area is seen.
Improper place-ment (if entire root is not cov-ered) will result in no apices appear-ing on the image.
Buccal object rule • a.k.a. tube shift technique • used to determine an object's spatial po-sition/buccal-lingual relationship within the jaws • two images are obtained, each exposed with a different angulation • used to compare the object's position with respect to a reference point (e.g., root of a tooth)
Example • if the PID is moved mesially and the ob-ject in the second image appears to have moved in the same direction, the object lies to the lingual • if the PID is moved mesially and the ob-ject in the second image appears to have moved in the opposite direction, the ob-ject lies to the buccal • use the acronym SLOB to remember the buccal object rule
In image #1, note the location of the object in reference to the mesial root of the first molar.
In image #2, the PID was moved mesially; the ob-ject in reference to the mesial root of the first molar has also moved mesially.
L - O - B RULE
Same = Lingual
Anu Singh
extraoral Identify the radiopaque areas labeled 1 & 2 on the image below.
Ghost image • defined as a radiopaque artifact on a panoramic image that is produced when a radiodense object is penetrated twice by the x-ray beam • occurs If all metallic or radiodense ob-jects (e.g., eyeglasses, earrings, necklaces, hairpins, removable partial dentures, com-plete dentures, orthodontic retainers, hear-ing aids, napkin chains) are not removed before exposure of panoramic receptor • obscures diagnostic information
Ghost image appearance • resembles its real counterpart • found on the opposite side of the image; appears indistinct, larger, & highepthan its actual counterpart • a ghost image of a hoop earring appears on the opposite side of the image as a ra-diopacity that is larger & higher than the real hoop earring; appears blurred in both horizontal and vertical directions • to avoid ghost images, instruct the pa-tient to remove all radiodense objects in the head-and-neck region prior to exposure of the panoramic receptor
The erupted permanent teeth are highlighted in gray in the charts below. Based on this in-formation, the panoramic film appears to represent a child of < 9 years old.
Permanent teeth eruption charts
Maxillary
Central incisor
Lateral incisor
Canine
First premolar
Second premolar
First molar
Second molar
Third molar
Age at eruption
7-8
8-9
11-12
10-12
10-12
6-7
12-13
17-21
Mandibular
Central incisor
Lateral incisor
Canine
First premolar
Second premolar
First molar
Second molar
Third molar
Age at eruption
6-7
7-8
9-10
10-12
11-12
6-7
11-13
17-21
tech Identify each one of the following that is an advantage of using the parallel-ing technique.
Parelling technique • based on concept of parallelism • preferred technique for intraoral films
Basic principles • receptor is placed parallel to the long axis of the tooth being imaged • central ray is directed perpendicular to both the receptor & long axis of the tooth • a beam alignment device must be used to keep the receptor parallel to the tooth • the object-receptor distance must be in-creased to keep the receptor and tooth paral-lel • the target-receptor distance must be in-creased to make certain the most parallel rays will be aimed at the tooth and receptor (16" target-receptor distance)
Long axis ol toolh
• accuracy • simplicity • duplication
Advantages • accuracy - image is highly representative of the actual tooth • simplicity - simple & easy to learn and use • duplication - easy to standardize and can be accurately duplicated when serial images are needed
Disadvantages • receptor placement - it may be difficult for operator to place the beam alignment device in some patients • discomfort - the beam alignment device may cause discomfort
^to Positions of the receptor, tooth and central ray in the paral->ft ^% leling technique. The receptor & long axis of the tooth are par-** »<*• allel. The central ray is perpendicular to the tooth and receptor.
An increased target-receptor distance (16") is required.
Bisecting technique • based on rule of isometry • technique used for periapicals
Basic principles • receptor must cover area of interest • receptor must be placed so 1/8" ex-tending beyond the occlusal or incisal surfaces • central ray is directed perpendicular to the imaginary bisector • central ray is directed through the contact areas of the teeth • x-ray beam must be centered over the receptor so that the entire receptor is ex-posed
• distortion • angulation problems
Advantages • can be used without a beam alignment device and therefore may be more read-ily accepted by patients • requires a shorter exposure time
Disadvantages • image distortion (magnification) oc-curs when a short (8") PTD is used • angulation problems may occur be-cause no beam alignment device is used resulting in images that are elongated or foreshortened
Length of image
The image on the receptor is equal to the length of the tooth when the central ray is perpendicular to the "imag-inary bisector". A short (8 ") target-receptor distance is required.
